Re: [PATCH v3 4/7] gpio: max7360: Add MAX7360 gpio support

["Mathieu Dubois-Briand" <mathieu.dubois-briand@bootlin.com>]

On Thu Feb 13, 2025 at 11:59 AM CET, Mathieu Dubois-Briand wrote:
> On Wed Feb 12, 2025 at 5:17 PM CET, Andy Shevchenko wrote:
> > On Wed, Feb 12, 2025 at 05:08:56PM +0100, Mathieu Dubois-Briand wrote:
> > > On Wed Feb 12, 2025 at 4:14 PM CET, Andy Shevchenko wrote:
> > > > On Wed, Feb 12, 2025 at 01:57:34PM +0100, Mathieu Dubois-Briand wrote:
> > > > > On Mon Jan 27, 2025 at 2:07 PM CET, Andy Shevchenko wrote:
> > > > > > On Mon, Jan 13, 2025 at 01:42:28PM +0100, Mathieu Dubois-Briand wrote:
> >
> > ...
> >
> > > > > > > +	if (of_property_read_u32(pdev->dev.of_node, "ngpios", &ngpios)) {
> > > > > > > +		dev_err(&pdev->dev, "Missing ngpios OF property\n");
> > > > > > > +		return -ENODEV;
> > > > > > > +	}
> > > > > >
> > > > > > This is not needed, it is already done in GPIOLIB core.
> > > > > 
> > > > > I believe this is still needed:
> > > > > - For gpos, we need the gpio count to correctly set the partition
> > > > >   between gpo and keypad columns in max7360_set_gpos_count().
> > > >
> > > > Shouldn't be that done somewhere in the GPIO valid mask initialisation?
> > > >
> > > > > - For gpios, we need the gpio count to setup the IRQs.
> > > >
> > > > Doesn't GPIOLIB parse the property before initializing the IRQ valid mask
> > > > and other init callbacks?
> > > 
> > > No, I believe I have to register the IRQ before registering the GPIO, so
> > > I can get the IRQ domain.
> > > 
> > > Right now I have something like:
> > > 
> > > irq_chip->num_irqs = ngpios;
> > > devm_regmap_add_irq_chip_fwnode(dev, dev_fwnode(dev), max7360_gpio->regmap,
> > > irq, flags, 0, irq_chip, &irq_chip_data);
> > > gpio_config.irq_domain = regmap_irq_get_domain(irq_chip_data);
> > > devm_gpio_regmap_register(dev, &gpio_config);
> > > 
> > > Also, gpiolib will store ngpios in the gpio_chip structure, but while
> > > using gpio-regmap, this structure is masked behind the opaque
> > > gpio_regmap structure. So I believe there is no easy way to retrieve its
> > > value.
> > > 
> > > This part of the code changed a lot, maybe it would be easier if I push
> > > a new version of the series and we continue the discussion there?
> >
> > So, what seems need to be added is some flag to GPIO regmap configuration
> > data structure and a code that is called after gpiochip_add_data() in
> > gpio_regmap_register() to create a domain. This will solve the above issue
> > and helps other drivers to get rid of potential duplication of
> > devm_regmap_add_irq_chip_fwnode() calls.
> >
> > Have you researched this path?
>
> OK, so looking at the code, I believe it would need to:
> - Add some flag in gpio_regmap_config structure, so
>   gpio_regmap_register() creates a new IRQ domain.
> - Add a function allowing to retrieve this domain out of the gpio_regmap
>   structure.
> - Allow to pass a domain in the regmap_irq_chip structure, so
>   regmap_add_irq_chip_fwnode() use this domain instead of calling
>   regmap_irq_create_domain().
> - Make sure this domain is still populated with the IRQ data: number of
>   IRQs, IRQ base but also a pointer on the regmap_irq_chip_data
>   structure in .host_data. I believe this will be a bit tricky.
> - Add a function allowing to retrieve ngpio out of the
>   gpio_regmap.gpio_chip structure, so it can be used for IRQ setup and
>   other places of the driver.
>
> I'm sorry, but I feel like this is a lot of changes to solve this point.
> I've been thinking about it, and I can suggest a different solution.
>
> For gpios, I will remove the ngpios property of the device tree and use
> a fixed value:
> - For the today version of the chip, this is always 8.
> - I a chip variant or a similar chip ever arise later with a different
>   number of gpios, the fixed value can be set according to the
>   "compatible" value.
> - This removes any issue with the IRQ setup.
>
> For gpos, we have to keep ngpios, as it depends of the implementation on
> the board. That means ngpios will be used:
> - For the gpio chip configuration: we let gpiolib retrieve it from the
>   device tree.
> - In gpio-regmap reg_mask_xlate callback: I can add a function allowing
>   to retrieve it from gpio_regmap.gpio_chip, as suggested above.
> - In max7360_set_gpos_count() to validate the coherency between
>   requested gpios and keypad columns and set the correct configuration
>   on the chip:
>   - I can also retrieve the value from gpio_regmap.gpio_chip, but that
>     means the check is made after the call to
>     devm_gpio_regmap_register().
>   - Or I will still need to retrieve it using device_property_read_u32()
>     here.
>
> How do you feel about this solution?

Actually there is an additional issue: today, relying on gpiolib to
parse the "ngpios" property does not work with gpio-regmap.

The gpiochip_get_ngpios() function in gpiolib is called in
gpiochip_add_data_with_key(), but when using gpio_regmap_register(),
we first ensure ngpio is set correctly before calling anything.

Yet I believe this check can safely be removed, allowing the magic in
gpiolib happen as expected.


-- 
Mathieu Dubois-Briand, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com